Vinyl aromatic compounds such as styrene and methyl styrene are important components in the petrochemical industry which can be employed to produce a wide variety of synthetic plastics and resins. An important example of styrene type monomers in polymerization reaction is in the polymerization of styrene to produce styrene homopolymers and copolymers. In the production of styrene, benzene is alkylated with ethylene in the presence of a suitable inorganic catalyst in order to produce ethylbenzene. The ethylbenzene is dehydrogenated in the presence of an inorganic dehydrogenation catalyst, typically based upon iron and potassium compounds such as ferric oxide and potassium oxide, to produce styrene.
Such dehydrogenation reactions may be carried out in radial flow dehydrogenation reactors. These reactors may take the form of vertically oriented cylindrical reactors having two or more concentric cylindrical shells which can vary in diameter from a few feet to perhaps twenty or thirty feet and which can extend vertically in length to an elevation of more than 100 feet. The ethylbenzene feedstock may be supplied along with a source of heat into the internal flow path of the radial flow reactor. Typically, superheated steam heated to a temperature of perhaps 500-850° C. is introduced into the reactor as a co-feed along with the ethylbenzene feedstock. The steam hydrocarbon mixture flows into the interior tubular member of the reactor and then outwardly through a bed of dehydrogenation catalyst disposed in the annular space between the interior reactor tube and an outer reactor shell. The product containing a mixture of styrene, ethylbenzene as well as hydrogen, steam and water is withdrawn from the top of the radial flow reactor and then passed to a second stage reactor in the reactor system. The input into the second reactor may be passed through a heater and additional steam may be introduced with the input into the second reactor where the feedstock again flows through a catalyst bed in an annular space surrounding the interior reactor tube to effect further dehydrogenation. Additional reactor stages can be employed. Typically, commercial systems employed in the dehydrogenation of ethylbenzene to produce styrene may comprise some 3 or 4 reactors. However, in some cases two series connected reactors are sufficient to achieve the desired styrene product and in other cases single stage reactor systems may be employed.